The present invention is directed in general to a telecommunication subnetwork system, and, more particularly, to a method of managing a SONET ring subnetwork through the use of a ring table that is embedded into each network element of the ring.
In telephone communications in the past, voice/data was carried primarily over metallic media such as twisted pair and coaxial cable. Over metallic media, voice/data is transferred at a speed or line rate of various levels. For example, the human voice can be carried as a digital signal at a line speed of 64 kilobits per second (kbps). For this line speed, the voice signal must be sampled 8,000 times each second, and using pulse code modulation, each voice value is carried as an eight-bit sample. This 64 kbps rate is called the Digital Signal level 0, or DS-0, rate. Higher rates, such as DS-1, DS-2, DS-3, . . . DS-N also exist, and are described in the International Telegraph and Telephone Consultative Committee (CCITT) Recommendations G.703. However, the speed at which data is transferred over metallic media is limited. To overcome this limitation, optical fiber media have been developed, which can accommodate much higher line speeds, and hence can transfer much more information in a given period of time.
The development of optical fiber transmission systems resulted in the Synchronous Optical NETwork or SONET standard, which is a Northern American version of SDH (Synchronous Digital Hierarchy). SONET defines a line rate hierarchy and frame format, and is fully described by the American National Standards Institute (ANSI) specification for a high-speed digital hierarchy for optical fiber communications in ANSI T1.105 and T1.106.
The SONET line rate hierarchy is based upon transmission building blocks of 51.84 million bits per second (Mbps) each. The 51.84 Mbps rate is called the Synchronous Transport Signal level 1 (STS-1), which is the basic logical building block. Higher rates or levels are all multiples of the basic rate of 51.84 Mbps, for example, the STS-3 rate is 155.52 Mbps. In general, the different line rates of the electrical signals are referred to as an STS-N rate. The different line rates of the optical signals corresponding to the electrical signals are referred to as OC-N.
The frame format for STS-N line rates is derived from a basic unit of transport for the STS-1 frame, which is organized into nine rows of 90 bytes or 810 bytes per frame. Each frame is generated 8,000 times per second (8 KHz), yielding the 51.84 Mbps STS-1 rate (i.e., 8000 frames/second * 810 bytes/frame * 8 bits/byte). By now, those skilled in the art are well familiar with the SONET standard, and thus further description thereof will be omitted.
Referring now to FIG. 1a, there is shown a high-level architecture of a typical telecommunication subnetwork system including a SONET ring 1, which is a collection of nodes or network elements (throughout this specification the terms "node" and "network element" are used interchangeably) N(1), N(2), . . . N(n) coupled together by optical fiber 2 to form a closed loop. The nodes N(1), N(2) are coupled to an operation support system (OSS), which performs the general telecommunication functions.
The nodes or network elements N(1) to N(n) are SONET add-drop multiplexed (ADM) providing access to all or at least a subset of the STS path signals contained within an OC-N optical channel of the optical fiber 2. As described later on in more detail, STS or VT (virtual tributary) signals are added to (inserted) or dropped from (extracted) the OC-N signal as it passes through the individual add-drop multiplexed nodes.
SONET rings can be divided into two general categories, namely, line switched and path switched according to the protection mechanism. Further, according to the direction of the traffic flow under normal working conditions, these categories are divided into unidirectional and bidirectional subcategories.
A line switched architecture uses SONET line layer indications to trigger the protection switching action. Switching action is performed at only the line layer to recover from failures, and does not involve path layer indications. Line layer indications include line layer failure conditions and signaling bit-coded messages that are sent between nodes to effect a coordinated line protection switch. In the event of a failure, line switched rings establish ring switches at the two nodes adjacent to the failure. In addition, four-fiber bidirectional line switched rings may have the capability of using span switching.
A path switched ring include two counter-rotating fibers, each of which forms a two-way communication-path. The duality of complete two-way paths is used to protect each other at any given time. The incoming tributary from the low speed side is permanently bridged at the node where it enters the ring and is transmitted in both directions over the different fibers to the node where the channel is dropped from the ring. At this node one of the two signals is selected as working. The trigger mechanism for the protection switch is derived from information in the SONET path layer.
In a unidirectional path switched ring, normal routing of the working traffic is such that two way communication signals travel around the single fiber of the ring in the same direction (e.g., clockwise). Specifically, the two way communication signals use capacity along the entire circumference of the ring.
FIG. 2 illustrates a unidirectional, two-fiber path switched SONET ring. The SONET ring has, for example, five nodes N(1) to N(5), which are interconnected by a unidirectional, two-fiber path having working W and protection P paths. In the unidirectional SONET ring, the incoming and outgoing data follow the same direction on the ring.
FIGS. 3a and 3b illustrate a bidirectional two-fiber and four-fiber line switched SONET ring, respectively. Here, normal routing of the working traffic is in both directions. That is, traffic traverses a ring normally carried on the working channels, except in the event of a ring or span protection switch, in which case it is restored on the protection channels.
In the two-fiber ring of FIG. 3a, a first optical fiber OF1 includes first working W1 and protection P1 channels and a second optical fiber OF2 includes second working W2 and protection P2 channels. In the four-fiber ring of FIG. 3b, the four optical fibers OF1 to OF4 form two pairs of bidirectional optical fibers, one pair being used for bidirectional working channels W1, W2, and the other pair being used for bidirectional protection channels P1, P2.
In a SONET ring configured in one of the manners described above, the transfer of data throughout the ring must be provisioned to achieve Time Slot Assignment (TSA), Time Slot Interchange (TSI), and all cross connections between the line side and add-drop side for each of the nodes in a ring. Generally, these ring provisioning techniques are carried out by many cross connection commands issued from the OSS to each of the individual nodes or network elements as shown in FIG. 1a.
A more recent requirement or demand from telecommunication service providers is that the provisioning process be performed by the individual network elements in response to provisioning information or commands provided by the OSS or other network management tools. This is commonly termed autoprovisioning.
Another requirement for SONET ring telecommunication subnetwork systems is that of automatic protection switching. Currently, in known telecommunication systems, the amount of provisioning information that is stored at each of the network elements is quite limited. For instance, according to one method, single cross connection assignment information is stored in each of the network elements. In this method, because the individual network elements only have isolated single termination assignment information, each of the individual cross connections is treated as an entity. In a second method, each network element includes cross connection information for a single node so that the node is treated as a managed entity. Both of these methods, however, are disadvantageous in that they rely on a centralized OSS to provision the individual network elements of the SONET ring.
In a telecommunication subnetwork system, such as that shown in FIG. 1a for example, all intelligence of the network management system resides primarily in the OSS. A subnetwork management layer is missing from the architectures known today. Moreover, in most cases, the network elements are simply "dummy" equipment and have little or no management functions at all. In other words, the OSS manages all operations and functions of the network elements by communicating commands to each of the network elements individually. As a result, the OSS is under a heavy burden to manage each of the individual network elements.
Thus, if this methodology in which the OSS is under a heavy burden to manage each of the individual network elements continues, it will lead to inefficient operation of the OSS and the SONET ring as a whole. Moreover, as the telecommunication subnetwork increases in size, as more SONET ring and/or individual network elements are added, and as more functions and services are provided, the OSS will not be able to manage the network in an effective manner.
As new SONET ring technologies and architectures evolve, the traditional network management methods will not be adequate. For example, a SONET ring must provide support for self-healing, autoprovisioning, software/firmware download, and provide quick responses to network management requests. The current centralized management method, which places a heavy burden on the OSS to meet all of these needs, is simply not adequate.
Thus, without partitioning and distributing the network management functions to the subnetwork and network element level, the situation will become even worse. There is thus a need to change from a more centralized to a more distributed managed network. The present invention as described herein meets this and all other requirements mentioned above.